安卓。读取外部存储文件

Question

我试图通过这个程序从外部存储中获取文件：

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView textView = findViewById(R.id.textView);
        StringBuilder builder = new StringBuilder();
        File specFile = Environment.getExternalStorageDirectory();

        builder.append(Environment.getExternalStorageState() + "\n");
        if (specFile.exists()) {
            builder.append(specFile);
            if (specFile.list() != null) {
                String[] files = specFile.list();
                for (int i = 0; i < files.length; i++) {
                    builder.append(files[i] +"\n");
                }
            } else {
                builder.append(" exist but empty\n");
            }
        }
        builder.append("/storage/emulated/0/Android exist: " + new File("/storage/emulated/0/Android").exists());
        textView.setText(builder);
    }
}

添加了此权限：

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

它在仿真器中运行良好，但在真实的电话中，当我试图获取列表时，它返回null。它通常也能在存储中找到脏东西。

Answer 1

通过添加以下代码解决问题：

int requestCode = 0;

if (Build.VERSION.SDK_INT >= 23) {
    if(checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED){
        requestPermissions(new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, requestCode);
    }
}